Hierarchical use of heterogeneous flash memories for high performance and durability

The use of NAND flash memory for building permanent storage has been increasing in many embedded systems due to idiosyncrasies such as non-volatility and low energy consumption. The persistent requirements for high storage capacity have given rise to the increase of bit density per cell as in multi-level cells but this has come at the expense of performance and has resulted in degradation of durability. In this paper, we introduce a complementary approach to boost the performance and durability of MLC-based storage systems by employing a non-volatile buffer that temporarily holds the data heading to MLCs. We also propose algorithms to efficiently eliminate unnecessary write and erase operations in MLCs by performing a pre-merge in the buffer. Our experiments show that the proposed approach can decrease average response time by up to 4 times and increase durability by 4 times by adding only a small hardware cost.